Field emission displays are known in the art. They include an envelope structure having an evacuated interspace region between two display plates. Electrons travel across the interspace region from a cathode plate (also known as a cathode), which includes electron-emitting devices, to an anode plate (also known as an anode), which includes deposits of light-emitting materials, or "phosphors". Typically, the pressure within the evacuated interspace region between the cathode and anode plates is on the order of 10.sup.-6 torr.
In order to provide a strong electric field (volts per unit distance between the plates) for acceleration of electrons toward the anode, while maintaining low power consumption, the distance between the cathode and anode plate is small, on the order of one millimeter. This proximity of the plates introduces the problem of potential electrical breakdown between the electron emitting surface and the inner surface of the anode plate. Such an electrical breakdown effectively ruins the display.
The cathode plate and anode plate are thin in order to provide low display weight and reduce package thickness. If the display area is small, such as in a 1" diagonal display, and a typical sheet of glass having a thickness of about 0.04" is utilized for the plates, the display will not collapse or bow significantly. However, as the display area increases the thin plates are not sufficient to withstand the pressure differential in order to prevent collapse or bowing upon evacuation of the interspace region. For example, a screen having a 30" diagonal will have several tons of atmospheric force exerted upon it. As a result of this tremendous pressure, spacers play an essential role in large area, light-weight displays. Spacers are structures being incorporated between the anode and the cathode plate, upon which electron-emitter structures, such as Spindt tips, are fabricated. The spacers, in conjunction with the thin, lightweight, plates, support the atmospheric pressure, allowing the display area to be increased with little or no increase in plate thickness.
Several schemes have been proposed to provide display spacers. These spacers and methods have several drawbacks. Methods for fabricating spacers which employ screen printing, stencil printing, or the use of glass balls suffer from the inability to provide a spacer having a sufficiently high aspect ratio (the ratio of spacer height to spacer thickness).
Other prior art methods for fabricating display spacers, such as reactive ion etching and plasma etching of deposited materials, suffer from slow throughput, slow etch rates, tapered spacer cross-sections, and etch mask degradation. Spacers comprised of lithographically defined photoactive organic compounds are not compatible with the high vacuum conditions within the display or with the elevated temperatures characteristic of the processes for manufacturing field emission flat panel displays.
Accordingly, there exists a need for a method for incorporating spacers into a field emission display which provides high throughput. There also exists a need for a spacer having a high aspect ratio which exhibits good perpendicularity with the anode and cathode plates, and which does not introduce off-gassing contaminants within the display.